1. Field of the Invention
The present invention relates to tire inflation pressure monitoring devices, and more particularly, to techniques for registering IDs of transmitters which transmit air pressure signals indicative of tire inflation pressures, detected by respective air pressure sensors, to a receiver.
2. Description of the Related Art
In recent years, various devices have been developed and put to practical use which are configured such that a plurality of items of air pressure information, obtained by tire pressure sensors arranged in respective tires of a motor vehicle, are transmitted as air pressure signals by radio from transmitters attached to the respective tires and are received by a receiver arranged in the vehicle. In this type of device, if any of the air pressure signals received by the receiver shows a value smaller than a predetermined value, a warning lamp arranged near the driver's seat (e.g., on the instrument panel) of the vehicle, for example, is switched on. Thus, the driver is warned that the tire inflation pressure needs to be increased.
The air pressure signal transmitted in such devices includes ID information of the individual transmitters (or tire pressure sensors), in addition to the air pressure information. The ID information of the transmitters is previously registered in the receiver at the time of shipment or replacement of tires. It is therefore possible to identify the tire whose air pressure has decreased.
Methods of registering the transmitters' IDs in the receiver include, for example, a method in which ID signals are forcedly transmitted from the tire pressure sensors by using a registration tool, and a method in which ID signals are transmitted, together with the air pressure signals, from the tire pressure sensors at periodic intervals during traveling.
The method of transmitting the ID signals from the transmitters and receiving the signals by the receiver is, however, associated with the problem described below. If, during ID registration, an ID signal is received together with an air pressure signal from a vehicle near the vehicle in question, for example, there is a possibility that the ID signal from the nearby vehicle is erroneously registered as a correct ID signal. Especially, in places where numerous vehicles exist, such as a vehicle shipment area or a vehicle maintenance area, it is likely that a vehicle is input with ID signals of other vehicles. This problem is often encountered when transmitters' IDs are registered in such places.
To solve the problem, there has been proposed a device in which, with respect to the transmitters associated with n tires of a vehicle, transmission order of ID signals is previously set as an ID sequence, and if the order of reception of the ID signals disagrees with the preset ID sequence, ID registration is not performed (cf. Unexamined Japanese Patent Publication No. 2002-131165).
There has also been proposed a device in which the transmitters associated with respective tires of a vehicle repeatedly transmit their ID signals at predetermined intervals of time, and if it is judged after a lapse of a predetermined time that the received ID signals show IDs greater than the number n of tires to be registered, the most frequently received n IDs are registered as proper tire ID (cf. Japanese Patent No. 3061047).
Further, a method has been proposed in which the tire inflation pressure is suddenly changed for a while to cause the tire pressure sensor to transmit the ID signal along with the air pressure signal.
However, the device disclosed in Unexamined Japanese Patent Publication No. 2002-131165 has the problem that the IDs fail to be registered if the order of reception of ID signals changes for some reason or other, though the number of ID signals is the same.
In the device disclosed in Japanese Patent No. 3061047, on the other hand, if a vehicle near the vehicle in question transmits ID signals with high frequency, the IDs from the nearby vehicle may possibly be registered in error. In such cases, it is necessary that the same ID signals be repeatedly received a number of times up to a certain frequency, which, however, requires considerable time for the ID registration.
Further, with the method in which the tire inflation pressure is suddenly changed for a while to cause the tire pressure sensor to transmit the ID signal along with the air pressure signal, there is a possibility that an ID signal received from a different vehicle running near the vehicle in question is registered in error.